Zoe A. D. Lethbridge

Brillouin scattering study on the single-crystal elastic properties of natrolite and analcime zeolites

The Brillouin light-scattering technique was used to investigate the single-crystal elastic properties of two aluminosilicate zeolites, natrolite (NAT) and analcime (ANA), at ambient conditions. An inversion of the acoustic velocity data results in the full set of elastic stiffness moduli (Cij’s) for both materials. From the single-crystal moduli the aggregate adiabatic bulk moduli (Ks), shear moduli (G), and Poisson’s ratios (ν) were found to be Ks=48.5(1.0)GPa, G=31.6(1.0)GPa, and ν=0.232(5) for NAT, and Ks=59.8(1.2)GPa, G=32.1(1.0)GPa, and ν=0.272(5) for ANA (Voigt-Reuss-Hill averages). The bulk and shear moduli of both zeolites are relatively low compared with those of densely packed aluminosilicates, reflecting an open framework structure of (Al,SiO4) tetrahedra which is easily deformed by bending the Si–O–Al angles. As expected for a less dense crystal, NAT is softer and more compressible than ANA. An evaluation of the directional Young’s moduli shows that the compressibility of NAT is nearly unifor...

Preparation and characterization of polyethylenimine-coated Fe3O4-MCM-48 nanocomposite particles as a novel agent for magnet-assisted transfection.

A new type of magnetic nanoparticle was synthesized using mesoporous silica MCM-48 as a template. Magnetite (Fe(3)O(4)) nanocrystals were incorporated onto the MCM-48 silica structure by thermal decomposition of iron(III) acetylacetonate. The particle size of these Fe(3)O(4)-MCM-48 composite particles is around 300 nm with an iron oxide content of ca. 20% w/w. Measurements from SQUID magnetometry suggest that these nanoparticles possess superparamagnetic properties similar to those of Fe(3)O(4) nanoparticles. By coating positively charged polyethylenimine on to the surface, DNA can be bound onto the Fe(3)O(4)-MCM-48 nanoparticles. Transfection studies showed that these PEI-Fe(3)O(4)-MCM-48 particles were highly effective as a transfection reagent, and a 400% increase of transfection efficiency compared with the commercial products was recorded.

Negative Poisson's ratios in siliceous zeolite MFI-silicalite

Brillouin scattering measurements of the single-crystal elastic properties of the as-made zeolite silicalite mid R:(C(3)H(7))(4)NFmid R:(4)[Si(96)O(192)]-MFI provides the first experimental evidence for on-axis negative Poissons ratios (auxeticity) in a synthetic zeolite structure. MFI laterally contracts when compressed and laterally expands when stretched along x(1) and x(2) directions in the (001) plane (nu(12)=-0.061, nu(21)=-0.051). The aggregate Poissons ratio of MFI, although positive, has an anomalously low value nu=0.175(3) compared to other silicate materials. These results suggest that the template-free MFI-silicalite [Si(96)O(192)] might have potential applications as tunable sieve where molecular discriminating characteristics are adjusted by application of stress along specific axes.

Polymorphism and variable structural dimensionality in the iron(III) phosphate oxalate system: a new polymorph of 3D [Fe2(HPO4)2(C2O4)(H2O)2]·2H2O and the layered material [Fe2(HPO4)2(C2O4)(H2O)2]

Two new iron (III) phosphate oxalates have been isolated under hydrothermal conditions as phase-pure samples and their crystal structures determined from single crystal X-ray diffraction. [Fe(2)(HPO(4))(2)(C(2)O(4))(H(2)O)(2)] x 2 H(2)O, I, is a polymorph of a known phase and differs in the local arrangement of hydrophosphate, oxalate and coordinated water about iron, presenting a mer orientation of three coordinated phosphates, rather than fac as previously seen. The structure of I is three-dimensionally connected with similar network connectivity to the known phase but different overall topology. [Fe(2)(HPO(4))(2)(C(2)O(4))(H(2)O)(2)], II, has a layered structure constructed from octahedral Fe(III) centres coordinated by hydrophosphate, oxalate and water in a fac arrangement. The amount of water used in synthesis is one of the key experimental parameters in stabilising one phase over the other. Thermogravimetric analysis shows that both I and II ultimately collapse into dense tridymite type FePO(4) above 600 degrees C and variable temperature powder XRD shows that this occurs via crystalline intermediate phases. Variable temperature magnetisation measurements show that both materials order antiferromagnetically at low temperatures, with similar Néel temperatures (approximately 29 K) despite their long-range structural differences.

An investigation of the properties of large crystals of the zeolites dodecasil-3C and ferrierite by high-temperature birefringence microscopy and X-ray diffraction

Optical birefringence has been measured as a function of temperature for two types of siliceous zeolite crystals that contain organic template molecules. The specimens were prepared using modified solvothermal synthesis to produce large (similar to 1 mm dimension) crystals. In the case of the clathrasil dodecasil-3C the material undergoes a first-order phase transition at similar to 433 K that is reversible after heating to 873 K and cooling to room temperature. Comparison with powder X-ray diffraction data from a bulk sample shows that this is a ferroelastic tetragonal (I (4) over bar 2d) to cubic (Fd (3) over barm) transition, which is supported by the functional form of temperature variation of the birefringence. There is apparently no loss of the organic template involved in this transition. For the zeolite ferrierite, the plate-like crystals show a pronounced domain-like structure, which, although not due to twinning, shows a distinctive optical birefringence change on heating, suggesting that variable concentrations of organic template might be present in different domain-like regions. In this material there is no evidence for a change in crystal symmetry up to 873 K (Pnnm), despite apparent loss of some organic template from the material which, in turn, gives rise to strain birefringence at the edges parallel to the [010] direction.